Colin and Chris Weir, who won £161m in the lottery, have donated £3.5m so far to the pro-independence campaign Yes Scotland. Photograph: Andrew Milligan/PA

Nearly 80% of donations to Scotland's pro-independence campaign over the past year came from EuroMillions lottery winners Colin and Chris Weir.

The Weirs, who won £161m in the EuroMillions lottery in 2011, have donated £2.5m to the Yes Scotland campaign since April last year. They gave a further £1m in its first year of operation, figures published by the campaign show.

In a letter published in the Scotsman last Thursday, the Weirs rejected allegations that they were duped into giving the money. "As lifelong supporters of independence, it would be strange if we did not support the Yes Scotland campaign," they wrote. "No one bullied or targeted us."

The Weirs said they had given the money to promote the debate on Scottish independence. "[Scots] aren't going to vote based on how much money we have given to a particular campaign – they will make their decision based on being well-informed. That's why we made the donations we did," they said, "to ensure there was the chance of an informed debate."

The figures from Yes Scotland also reveal that five other donors have given more than £7,500 each, including Dan Macdonald,a property developer and member of Yes Scotland's advisory board, and Mark Shaw, director of operations for the campaign. Both gave £50,000. A Scottish National party activist, Randall Foggie, gave £60,000; the author and poet Mary McCabe gave £8,000, and another donor, Norman Easton, gave £10,000, taking the total for larger individual donations to £2,678,000.

This is the second voluntary publication of campaign donations by Yes Scotland and comes days before the SNP reveals its latest donors in an Electoral Commission quarterly report.

The pro-union Better Together campaign released its second round of donor information in December, and has since called for its counterpart to do the same. It

Better Together claimed the yes campaign's figures proved the party had little support beyond the SNP.

Blair MacDougall, Better Together's campaign director, said: "We now know why they have been hiding their donations for so long. Whilst Better Together relies on the support of a broad mixture of large donors and thousands of ordinary people giving what they can, it is clear that the nationalists are almost completely dependent on one source of income."

Its own report showed that 19 backers – including Conservative party donors, bankers and businesspeople linked to the intelligence services – had donated a total of £1.3m. These included £10,000 each from two senior figures in the private intelligence firm Hakluyt, which has links to MI6; £600,000 from the hotel and distilleries tycoon Donald Houston and his companies, and £23,000 from Sir John "Chips" Keswick, chairman of Arsenal FC and a Tory donor.

It also confirmed that more than 17,000 people had donated smaller amounts to the campaign. On Saturday, Yes Scotland said 11,000 donors had each given up to £7,500, making a total of £473,000.

• This article was amended on 11 May 2014. It originally stated that nearly 85% of donations came from the Weirs. This has been corrected to 79%.